silvia medri university of bologna

Analysis of the accuracy of Argus in identifying shoreline position:

comparison of two procedures with in-situ measurements in Lido di

Dante

Silvia Medri

University of Bologna

CoastView Meeting

Lisbon 18 – 19 Sept 2004

Contents1. Comparison of two procedures to find waterline

Description of the two procedures Justification of the use of the two procedures Results presentation Comments

2. Comparison of the two procedures in the study of shoreline evolution Results presentation Comments

3. Comparison of the two procedures with in-situ measurements Fieldwork description: GPS Survey, 15-22 July 2004 GPS survey data GPS-Argus Comparison Conclusions

1. Comparison of the two procedures

Description: first procedure First merge images with AMT

Then find WL with IBM


Description: second procedure

First find WL with IBM on single oblique images

Then “merge” single cameras WLs in a unique WL with Matlab.


Justification of the use of the two procedures Discrepancies at a qualitative inspection between obtained WLs Tidal levels assignment Operative differences

1st procedure: First merge then use IBM

2nd procedure: First use IBM then merge

Advantages:- accurate in the ROI overlap- accurate in identifying obstacles in the far field- at the present level of implementation fast

Advantages:- proper tidal level for each image- accurate in identifying details, due to the greater pixel resolution

Disadvantages:- approximated tidal levels- decrease of visualization of small objects (persons, umbrellas, etc..)- less image definition

Disadvantages:- not accurate in the region of cameras overlap- decrease of the possibility of identifying oblique obstacles-pixel resolution loss in the far field- at the present level of implementation slow


Presentation of resultsShoreline at the same hour obtained with the two procedures. [20 July 2004 06 GMT]


Reasons for a reduced area of calculations

Decreasing pixel resolution

worse representation of far field pixel intensities in dry/wet separation procedure

increase of the difficulty for the operator to visually distinguish the shoreline itself

WL position differences are calculated on the X axis of Argus reference system

overestimate these differences where the shoreline is not parallel to Y axis

Systematic tidal data delay

Whole area Reduced area


Statistics of differencesWLs at the same hour obtained with the two procedures for one day of the fieldwork. [20 July 2004 from 06 to 14:00 GMT]

WL Differences for the whole area

MAX MIN MEAN MEDIAN ST.DEV MEDIAN ABS4.58 -5.17 1.04 0.97 1.53 1.273.57 -10.28 -0.22 0.79 2.34 1.161.95 -5.97 -0.40 0.20 1.49 0.590.85 -1.43 -0.21 -0.10 0.50 0.330.91 -1.79 -0.52 -0.38 0.58 0.470.21 -2.11 -0.75 -0.64 0.51 0.642.51 -1.51 -0.27 -0.55 0.85 0.740.73 -1.50 -0.28 -0.25 0.63 0.400.78 -1.44 -0.33 -0.17 0.54 0.35

WL Differences for the reduced area

MAX MIN MEAN MEDIAN ST.DEV MEDIAN ABS2.42 -0.14 1.19 1.24 0.69 1.241.44 -3.59 0.06 0.93 1.73 1.121.25 -2.31 -0.36 0.08 0.93 0.420.68 -1.43 -0.26 -0.07 0.57 0.320.36 -1.26 -0.40 -0.23 0.44 0.290.20 -1.28 -0.56 -0.56 0.28 0.560.66 -1.51 -0.64 -0.66 0.39 0.660.73 -1.29 -0.29 -0.33 0.40 0.380.78 -1.30 -0.12 -0.05 0.45 0.33


Statistics of differences

WLs at the hour obtained with the two procedures for the whole period of the fieldwork. [ From 15 July to 22 July 2004]

Comparison between the two procedure for the entire period of the fieldwork

Statistic analysis of the differences on overall dataset of 35 shorelines each procedure

Parameter Whole area Reduced area

Mean of the MEANs -0.19 -0.14

Mean of the MEDIANs -0.07 -0.05

Mean of the MEDIANs of the Abs values 0.58 0.57

The Mean value of the Median of the absolute values of the differences between shorelines obtained with the two procedures indicates the two procedures disagree of about 0.58 m in both the whole and the reduced areas.


Comments The quantified disagreement between the two procedures (of

0.6 m) is not so important if compared with shoreline dynamics itself.

Against the expectation there aren’t significant improvements/variations in reducing the area of work.

? Probably the two systematic errors in timing the merged images and tide hide the differences.

There is a recurrent presence of outliers especially at the end of the area (due to unavoidable decreasing pixel resolution in the far field) and near the central groin (due to a significant density in that area of tourists and big umbrellas).

2. Comparison of the two procedures in the study of shoreline evolution

Presentation of resultsShoreline evolution during 1 day of the fieldwork with the two procedures. [20 July 2004 from 06 to 15 GMT]


Statistics of shoreline evolutionShoreline evolution during 1 day of the fieldwork with the two procedures calculated for the whole area and for the reduced area [20 July 2004 from 06 to 15 GMT]

WL displacements with the 1st procedureWhole area Reduced area

GMT MAX MIN MEAN MEDIAN STD MEDIAN ABS ZTIDE2 ZTIDE(2-1) MAX MIN MEAN MEDIAN STD MEDIAN ABS ZTIDE2 ZTIDE(2-1)

06 -07 2.22 -0.30 1.00 1.00 0.50 1.00 -0.35 0.12 2.09 0.36 1.04 1.02 0.39 1.02 -0.35 0.1207- 08 10.64 0.36 4.82 4.58 2.05 4.58 -0.07 0.28 5.70 4.00 4.65 4.55 0.44 4.55 -0.07 0.2808-09 5.30 -0.37 1.14 1.03 0.89 1.03 0.04 0.11 1.86 0.09 1.11 1.10 0.34 1.10 0.04 0.1109-10 2.03 -2.54 0.35 0.46 0.82 0.65 0.15 0.11 1.48 -0.07 0.50 0.51 0.35 0.51 0.15 0.1110-11 2.03 -0.66 0.36 0.18 0.61 0.40 0.20 0.05 1.37 -0.62 0.26 0.10 0.50 0.26 0.20 0.0511-12 1.80 -1.48 0.07 -0.03 0.71 0.42 0.19 -0.01 0.68 -1.48 -0.32 -0.27 0.46 0.33 0.19 -0.0112-13 1.19 -2.40 -0.31 0.00 0.86 0.61 0.14 -0.05 1.19 -0.17 0.39 0.36 0.33 0.36 0.14 -0.0513-14 0.48 -2.12 -0.59 -0.67 0.69 0.67 0.06 -0.08 0.48 -2.12 -0.42 -0.15 0.70 0.24 0.06 -0.08

WL displacements with the 2nd procedureWhole area Reduced area

GMT MAX MIN MEAN MEDIAN STD MEDIAN ABS ZTIDE2 ZTIDE(2-1) MAX MIN MEAN MEDIAN STD MEDIAN ABS ZTIDE2 ZTIDE(2-1)

06 -07 5.40 0.54 2.23 1.88 1.06 1.88 -0.35 0.12 4.67 0.54 2.27 1.85 1.13 1.85 -0.35 0.1207- 08 11.34 2.43 5.38 5.27 1.58 5.27 -0.07 0.28 8.71 2.55 5.20 5.23 1.30 5.23 -0.07 0.2808-09 4.07 -2.29 0.68 0.74 0.76 0.79 0.04 0.11 1.83 -0.35 0.73 0.73 0.45 0.73 0.04 0.1109-10 3.16 -0.06 0.83 0.82 0.44 0.82 0.15 0.11 1.99 -0.06 0.82 0.82 0.42 0.82 0.15 0.1110-11 2.02 -1.85 0.28 0.24 0.55 0.30 0.20 0.05 1.43 -0.60 0.27 0.24 0.34 0.26 0.20 0.0511-12 0.78 -2.84 -0.33 -0.13 0.64 0.18 0.19 -0.01 0.78 -1.25 -0.12 -0.09 0.30 0.15 0.19 -0.0112-13 0.75 -1.41 -0.28 -0.23 0.33 0.26 0.14 -0.05 0.69 -1.09 -0.25 -0.15 0.28 0.16 0.14 -0.0513-14 2.36 -1.64 -0.33 -0.39 0.53 0.45 0.06 -0.08 0.47 -1.15 -0.35 -0.51 0.39 0.51 0.06 -0.08


Analysis of WL displacements quality 1st criterion: to verify if the WL variation is coherent

in sign with the corresponding tidal level variation, indicating a clear trend of WL evolution (minimum requirement).

2nd criterion: to verify, in the unavoidable presence of small discrepancies (only few points in against trend), if however:

|Median - Median abs| < 0.1 m indicating a low percentage and a small entity of

values in against trend. In these cases the signs of shoreline displacements are

concordant among them, reproducing a mean intertidal beach profile with a constant sign slope (further requirement).

2. Comparison of the two proceduresEstimated mean intertidal beach profiles

The profiles show a qualitative good agreement with the realistic situation, in particular it is shown a simple morphology with lack of significant bars and throughs (Lido di Dante protected area)

WLs evolution for every day of the fieldwork with the two procedures calculated for both the whole and the reduced area


Statistics of shoreline evolution

EVALUATION OF THE QUALITY OF THE TWO PROCEDURES ON THE BASIS OF THE RESULTS OF SHORELINE EVOLUTION

Considered VERY GOOD RESULTS FAIRLY GOOD RESULTS BAD RESULTSarea Mean WL displacement coherent Mean WL displacement coherent Mean WL displacement

with the tidal level variation with the tidal level variation NOT coherent with the|median - median abs| < 0.1 m. |median - median abs| > 0.1 m. tidal level variation

Whole area MERGE 60% MERGE 32% MERGE 8%

SINGLE 79% SINGLE 15% SINGLE 6%

Reduced area MERGE 64% MERGE 28% MERGE 8%

SINGLE 88% SINGLE 6% SINGLE 6%


Comments on shoreline evolution In the whole area:

The 1st procedure (First merge then use IBM) gives results in very good agreement with the tidal excursion in about 60% of the instances, and fairly good results in about 30% of the instances in whom it was used.

The 2nd procedure (First use IBM then merge) gives results in very good agreement with the tidal excursion in about 79% of the instances and fairly good results in about 15% of the instances on whom it was used.

In the reduced area: The 1st procedure (First merge then use IBM) gives results in very good

agreement with the tidal excursion in about 64% of the instances in whom it was used, with a small improvement with respect to the whole area.

The 2nd procedure (First use IBM then merge) gives results in very good agreement with the tidal excursion in about 88% of the instances in whom it was used, with a small improvement with respect to the whole area.


Conclusions on shoreline evolution

Considering only ‘very good’ results, the 2nd procedure (SINGLE) is better then the 1st one (MERGE).

Considering the whole of ‘very good’ + ‘fairly good’ results, both the procedures are equivalently of high quality in the great part (about 90%) of the instances.

Both the procedures improve their performance in the reduced area.

Robustness test: the 2nd procedure is the most robust because it gives better results even in the whole area where there are the great part of outliers.

3. Comparison with in-situ measurements

Objectives To validate video derived data To provide demonstration CSIs for the Lido di Dante site. To check what is the best way to use Argus IBM.

Strategy To compare a significant set of surveyed shorelines with the

corresponding Argus waterlines, in order to evaluate the capability of Argus in identifying WLs for both the analysed procedures

To measure a significant set of surveyed cross-shore transects in order to have a more realistic estimate of intertidal beach slope.


Area of interest

40 shorelines 15 July (GMT 09:00, 11:00, 12:00 = 3 WL) 19July (from GMT 09:00 to GMT 16:00 = 7 WL) 20 July (from GMT 06:00 to GMT 15:00 = 10 WL) 21 July (from GMT 07:00 to GMT 16:00 = 10 WL) 22 July (from GMT 06:00 to GMT 15:00 = 10 WL)

60 transects15 July ( 2 transects)19July (11 transects)20 July (10 transects)21 July (12 transects)22 July (25 transects)

Available data set

15-22 July 2004 GPS Survey


GPS Technical Specifications: LEICA SR510

ReceiverSatellite Reception: single-frequency Receiver Channels: 12 L1 continuous tracking L1 channels: Carrier phase, C/A narrow L1 Carrier Tracking: reconstructed carrier phase via C/A

codeSatellites tracked: up to 12 simultaneouslyKinematic Mode : after a static or known point

initialisation, kinematic surveys can be carried out and with dynamic procedures in post processing yields 10 to 20mm + 2ppm rms

AntennaThe AT501 is a small precision centered L1 antenna ,L1 microstrip with Built-in groundplane .

CORS: Continously Operating Reference StationManager: Prof. Susanna Zerbini, Dept. of Geophysic,

University of Bologna. Position: Marina di Ravenna (8 Km far from Lido di Dante site)Data collection rate: 30 sec



Shoreline surveyed hourly basis, simultaneously with the recording of time-averaged video images by the 4-cameras of Argus video station in LdD.



Offshore Wave height (Hrms) in the period of the fieldwork: 15-22 July 2004

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

14/7/04 0.00

15/7/04 0.00

16/7/04 0.00

17/7/04 0.00

18/7/04 0.00

19/7/04 0.00

20/7/04 0.00

21/7/04 0.00

22/7/04 0.00

23/7/04 0.00

Date

Hrm

s (m

)

Ancona Punta della Maestra

Offshore Wave Heights range: (0.07 ÷ 0.5) meters



Wind DirectionWind Direction (°N)(°N)

Temperature Temperature (°C)(°C)

Wind DirectionWind Direction (°N)(°N)

Sea Water LevelSea Water Level (m)(m)

Atmospheric PressureAtmospheric Pressure (hPa)(hPa)

Water temperatureWater temperature (°C)(°C)

Wind IntensityWind Intensity (m/s)(m/s)

Tidal level range: -0.5 ÷ +0.3 meters


Presentation of results

3. Comparison with in-situ measurements 1st procedure (First merge then use IBM) – GPS Comparison

Time m Std Rms M Md Ma

20040715.gmt09 -0.25 0.91 0.94 -0.27 0.47 0.4220040715.gmt11 -0.48 0.88 1.01 -0.35 0.64 0.6920040715.gmt12 0.70 1.21 1.40 0.33 0.60 0.7520040719.gmt10 -0.73 0.81 1.09 -0.80 0.48 0.9620040719.gmt12 -0.13 0.97 0.98 -0.04 0.82 0.8120040719.gmt13 -0.11 0.83 0.84 -0.06 0.78 0.7920040719.gmt14 -0.22 1.47 1.49 0.07 0.76 0.7920040719.gmt16 0.14 1.05 1.06 0.41 0.89 0.8220040720.gmt06 0.81 1.49 1.70 1.31 0.52 1.4220040720.gmt07 -0.09 1.58 1.58 0.39 0.57 0.8320040720.gmt08 -0.92 1.38 1.66 -1.08 0.93 1.2820040720.gmt09 -0.74 0.98 1.23 -0.66 0.50 0.7520040720.gmt10 0.15 1.16 1.17 0.45 0.53 0.7820040720.gmt11 0.40 0.65 0.77 0.44 0.47 0.5220040720.gmt12 0.22 0.72 0.75 0.34 0.42 0.5820040720.gmt14 0.66 0.72 0.97 0.84 0.53 0.8420040721.gmt09 0.62 0.64 0.89 0.75 0.39 0.7620040721.gmt10 -0.14 0.62 0.64 -0.12 0.46 0.4620040721.gmt12 0.08 1.15 1.15 0.03 0.53 0.5120040721.gmt14 -0.62 0.68 0.92 -0.71 0.53 0.7620040721.gmt15 0.35 0.58 0.68 0.34 0.39 0.5520040721.gmt16 -0.25 0.64 0.68 -0.41 0.39 0.5120040722.gmt08 0.63 1.12 1.29 0.68 0.72 1.1020040722.gmt09 -0.29 0.85 0.90 -0.12 0.55 0.5720040722.gmt10 -0.45 1.00 1.10 -0.59 0.60 0.8120040722.gmt11 0.20 0.95 0.98 0.37 0.42 0.5520040722.gmt12 -0.07 0.56 0.56 -0.03 0.29 0.3120040722.gmt15 0.14 1.06 1.07 0.27 0.99 0.88

Mean -0.01 0.95 0.06 0.58 0.74

Std 0.47

Legenda

m = nanmean(Xi2(u)-Xi1(u))mean difference

Std = nanstd(Xi2(u)-Xi1(u)) Standard Deviation of differences

Rms = Sqrt(m^2+Std^2) Root mean square difference

M = nanmedian(Xi2(u)-Xi1(u)) Median difference

Md = nanmedian(abs(Xi2(u)-Xi1(u)-M)) Median Deviation

Ma = nanmedian(abs(Xi2(u)-Xi1(u))) Median Absolute difference

Xi1(u)= ARGUS wlXi2(u)= GPS wlu = parameter which definines the area of calculation


Time m Std Rms M Md Ma

15Jul04gmt09 0.35 0.93 0.99 0.37 0.73 0.6815Jul04gmt11 0.27 1.04 1.07 0.29 0.73 0.7315Jul04gmt12 0.54 1.26 1.37 0.32 0.46 0.4819Jul04gmt09 0.05 1.25 1.25 0.20 0.74 0.6919Jul04gmt10 0.53 1.10 1.22 0.48 0.81 0.6919Jul04gmt12 0.12 0.63 0.64 0.19 0.44 0.4819Jul04gmt13 0.46 0.73 0.86 0.58 0.63 0.6419Jul04gmt14 -0.13 1.15 1.16 -0.02 0.51 0.4919Jul04gmt15 0.69 0.96 1.18 1.00 0.61 1.0819Jul04gmt16 0.04 0.98 0.98 0.13 0.68 0.6420Jul04gmt06 0.08 1.11 1.11 -0.11 0.69 0.8020Jul04gmt07 0.20 1.96 1.97 -0.25 1.19 1.4220Jul04gmt09 -0.33 1.70 1.73 -0.18 0.98 0.9220Jul04gmt10 0.25 1.01 1.04 0.19 0.67 0.6420Jul04gmt12 0.81 1.27 1.50 0.92 0.53 0.9320Jul04gmt14 0.56 0.82 0.99 0.64 0.60 0.7421Jul04gmt09 0.63 0.91 1.10 0.47 0.42 0.5421Jul04gmt10 0.17 1.04 1.06 0.11 0.48 0.5421Jul04gmt14 -0.28 0.44 0.52 -0.25 0.35 0.3121Jul04gmt16 -0.09 0.63 0.63 -0.04 0.32 0.3222Jul04gmt06 0.97 1.40 1.71 1.03 1.17 1.4422Jul04gmt07 1.51 1.82 2.37 1.30 1.33 1.3422Jul04gmt08 0.84 1.23 1.49 1.01 0.95 1.2522Jul04gmt10 0.49 1.13 1.23 0.61 0.68 0.9022Jul04gmt11 0.64 0.91 1.11 0.68 0.48 0.7622Jul04gmt12 0.37 0.84 0.92 0.45 0.35 0.4822Jul04gmt13 0.39 0.73 0.83 0.58 0.42 0.6622Jul04gmt14 -0.23 1.05 1.07 -0.14 0.53 0.5722Jul04gmt15 0.23 0.86 0.89 0.36 0.55 0.59

Mean 0.35 1.07 0.38 0.66 0.75

Std 0.41

2nd procedure (First use IBM then merge) – GPS Comparison

Legenda

m = nanmean(Xi2(u)-Xi1(u))mean difference

Std = nanstd(Xi2(u)-Xi1(u)) Standard Deviation of differences

Rms = Sqrt(m^2+Std^2) Root mean square difference

M = nanmedian(Xi2(u)-Xi1(u)) Median difference

Md = nanmedian(abs(Xi2(u)-Xi1(u)-M)) Median Deviation

Ma = nanmedian(abs(Xi2(u)-Xi1(u))) Median Absolute difference

Xi1(u)= ARGUS wlXi2(u)= GPS wlu = parameter which definines the area of calculation


GPS - Argus Comparison

Results

The two procedures are equivalent on a set of normal (without spurious results) data. If there are significant outliers the 1st procedure seems better than the 2nd one.

Procedure Parameter m Std M Ma

1st :WL on MERGED planview images Mean of the parameter -0.01 0.95 0.06 0.74

2nd : WL on SINGLE oblique images Mean of the parameter 0.35 1.07 0.38 0.75


Comments

Result interpretation: the combined effect of two systematic errors in timing the merged images and tide results in hiding the great part of differences on merged images (1st procedure), while frustrating the precision in the synchronism with tidal data of oblique images (2nd procedure).

Result judgement: there is a good agreement of both the used Argus procedures to find shoreline location with ground truth data of GPS survey, considered the shoreline dynamics itself and the time shift in tidal data. (With correct tide data the 1st procedure is expected to give the better results (with a dispersion <0.5 m )).


Future work

To estimate the systematic error in our tide data by comparison with local measured data (past intensive fieldwork).

To estimate intertidal beach slope through the analysis of GPS intertidal transects.

To compare the two Argus procedures with GPS data even in the reduced area.

To carry out another GPS survey in October to have “cleaner” shorelines.

2. Shoreline Variation due to a storm Topographical Survey - O8 Oct 2003

TopographersNourishment works


July 2004 GPS Survey


15-22 July 2004 GPS SurveyAvailable data set

40 shoreline : 15 July (GMT 09:00, 11:00, 12:00 = 3 WL) 19July (from GMT 09:00 to GMT 16:00 = 7 WL) 20 July (from GMT 06:00 to GMT 15:00 = 10 WL) 21 July (from GMT 07:00 to GMT 16:00 = 10 WL) 22 July (from GMT 06:00 to GMT 15:00 = 10 WL)

60 transects 15 July ( 2 transects) 19July (11 transects) 20 July (10 transects) 21 July (12 transects) 22 July (25 transects)

silvia medri university of bologna

Documents

procedures justification

wl position differences

gmtfoglio1wl differences

shoreline position

unique wl

reduced areamaxminmeanmedianst

accuracy of argus

reduced areas